FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10, rule 13)
“SYSTEM AND METHOD FOR GENERATING A CONSTANT CURRENT AND CONTROLLING THE SAME TO DRIVE AN INDUCTIVE LOAD”
MINDA CORPORATION LIMITED of E-5/2, Chakan Industrial Area, Phase- III M.I.D.C. Nanekarwadi, Pune, Maharashtra, 410-501, India
The following specification particularly describes the invention.

Field of the Invention
The Present disclosure relates to an electronic circuit. Particularly, the present disclosure relates to an electronic circuit f or a system that drives reasonably constant current from a current source through an inductive load, and also relates to a method for generating a constant magnetic field around the load using said electronic circuit.
Background
Applications requiring generation of a Low Frequency Magnetic field (LF) for applications such as proximity sensing for vehicle access, need to drive reasonably constant current square waveform through a solenoid coil forming an inductive load. This required to ensure constant proximity sensing distance for sensing the proximity of the target. Thus, there exists a need for developing a low-cost novel system and method that generates and drives a reasonably constant current for such application where it is required to ensure reasonably constant proximity sensing distance.
The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Summary of the invention:
One aspect of the present invention relates to a system and method for generating and controlling a constant current to drive an inductive load. Particularly, the system configured to generate a constant current irrespective of any variation in the input voltage and load resistance and controls the current to drive the inductive load. The system comprising a transistorized current source and a MOSFET H-Bridge driven by a micro controller. The transistorized current source generates a constant current that

configured to drive an inductive load such as solenoid. The MOSFET H-bridge coupled with the micro controller configured to control the flow and direction of the current into the inductive load and thereby ensures safe driving of the load.
Other aspect of the present invention relates to a method of generating a constant magnetic field around an inductive load, the method comprising: receiving, at a driving unit (104), a constant current generated from a constant current source (101); receiving, at the driving unit (104), a control signal from a controller (103); and driving, by the driving unit (104), the inductive load based on said received constant current and the control signal to generate the constant magnetic field around the inductive load, wherein driving the inductive load based on received constant current and the control signal comprising: allowing, by a driving unit (104), the constant current to flow across the inductive load (ZL); and controlling, by the controller, the driving unit to alter the current flow direction between two opposite sides of the inductive load so that the constant current alternatively pass through the opposite sides of the inductive load between a predetermined interval.
Some another aspect of the present invention relates to a system for generating and controlling a constant current to drive an inductive load (ZL), comprising: a power supply; a constant current source (101) connected in series with the power supply, the constant current source configured to generate a constant current irrespective to any variation in the power supply voltage; and a controller (103) configured to generate a control signal; and a driving unit (102) coupled to the controller (103) and configured to drive the inductive load based on said control signal using the said constant current.
Brief description of the Accompanying Drawings:
Further aspects and advantages of the present invention will be readily understood from the following detailed description with reference to the accompanying drawings where

like reference numerals refer to identical or similar or functionally similar elements. The figures together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the aspects/embodiments and explain various principles and advantages, in accordance with the present invention wherein:
Figure 1 illustrates a schematic diagram of a system for generating and controlling a constant current to drive an inductive load
Figure 2 illustrates an exemplary circuit diagram of a system depicted in Figure 1. Figure 3 illustrates a method aspect of the claimed invention explained in the form of a flow chart that particularly discloses the method of generating a constant magnetic field around an inductive load.
Detailed Description of the invention:
Referring now to the drawings, there is shown an illustrative embodiment of a system for generating a constant current and controlling the same to drive an inductive load. It should be understood that the invention is susceptible to various modifications and alternative forms; specific embodiments thereof have been shown by way of example in the drawings and will be described in detail below. It will be appreciated as the description proceeds that the invention may be used in various types of applications other than as mentioned in the present disclosure and may be realized in different embodiments.
The terms “comprises”, “comprising”, “including”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device, apparatus, system that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such setup or device or apparatus or system.

The present invention will be described herein below with reference to the accompanying drawings. In the following description well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail.
Fig 1 shows a schematic diagram of a system for generating and controlling a constant current to drive an inductive load. The system (100) comprising the inductive solenoid denoted by ZL needs to be driven with constant current of square wave (both half cycles equal in amplitude but opposite in polarity). This ensures that magnetic field strength at a given distance for proximity sensing is stable irrespective of changes in battery voltage. Typical application is proximity sensing of an authorized driver who needs to be authenticated for vehicle access (and eventually prevent theft).
The embodiment of the system as disclosed in Fig. 1 comprises a power supply, a constant current source (101) connected in series with the power supply, a controller (103) and a driving unit (102) coupled to the controller (103). The current source (101) configured to generate a constant current irrespective to any change or variation in the power supply voltage. The controller (103) configured to generate the control signal and the driving unit configured to drive the inductive load (ZL) based on said current and the control signal. For example, the driving unit is configured to drive the inductive load (ZL) by allowing the constant current to flow across the inductive load (ZL) based on said control signal received from the Controller. In an embodiment, as shown in Fig. 2, the system may comprises a H-Bridge circuit as a driving unit and a CPU as a control unit (103) so that the CPU’s control outputs, i.e., control output 1 and control output 2 alternately operate two arms of an H-Bridge to control the current through the inductive load (ZL). This is explained in detail below. Person skilled in the art may note that the circuit and/or the components shown in the Fig. 2 is just for exemplary purpose and would not limit the scope of this invention, as the system (100) may comprises any other similar components and/or circuit to achieve the desired purpose. For example,

the Fig. 2 shows a BJT based power source and MOSFET based H-Bridge. However, the power source and the H-Bridge may be formed using similar components to achieve the desired purpose.
The constant current source in series with the supply voltage ensures that the current drawn by the load is limited to a prescribed value. This prescribed value can be tuned by tuning appropriate component values for the current source. The impedance ZL comprises an inductance with its inherent resistance. When the proximity sensing is to be disabled as per application requirement then CPU operates both the bridges in “off” condition. This ensures near zero current through the load, conserving the battery current during such situations.
Figure 2 illustrates an exemplary circuit diagram of the system 100 shown in Figure 1. Accordingly, as show in the system of Figure 2, the Bipolar Junction Transistors T1, T2 and resistors Rt1 and Rt2 form a constant current source. In terms of connections among them, as shown in Fig. 2, a base terminal of T2 is connected to an emitter terminal of the T1 and a collector of the T2 is connected to a base of the T1. Further, the control unit is connected at the emitter terminal of the T2 and the power supply is connected to the collector terminal of the T1. Further, the Rt1 is connected between the base and collector terminals of the T1, and the Rt2 is connected between the base and emitter terminals of the T2. This way of connections of the components within the transistorized current source (101) enables the T2 to maintain the voltage across Rt2 limited to around one diode drop (base emitter diode). Whenever the load current tends to exceed this drop, it conducts more diverting the base current of the main current carrying transistor T1 thus restoring the current to a stable value given by Vbe/Rt2. Resistor Rt2 can be tuned to obtain the prescribed constant current required by the application. Person skilled in the art may note that in an alternate embodiment, at least any one of the two transistors T1 and T2 can be replaced with the MOSFET to achieve the desired purpose.

MOSFETs Q1, Q2, Q3 and Q4 form an H-Bridge. CPU operates diagonally opposite MOSFETs, thus pumping alternately opposite polarity currents. Diodes D1 through D4 and resistors R1 through R4 form gate interface circuits so that gate capacitance finds low resistance discharge paths through diode. The resistors limit charging inrush currents through the gate. Thereby, the H-bridge coupled with the CPU smartly controls the flow and direction of the current into the inducive load based on CPU control outputs to ensures safe driving of the load. Thus, in this way controller configured to control the driving unit to alter the current flow direction between two opposite sides so that the constant current alternatively pass through the opposite sides of the inductive load between a predetermined interval and generates a constant magnetic field strength around the load. For example while, the control output 1 or control signal 1 from CPU activates the MOSFETs Q1 and Q3 to allow the constant current to pass through the inductive load from right to left side, the control output 2 or control signal 2 from CPU after a predetermined time interval from control output 1 or control signal 1 from CPU activates the MOSFETs Q2 and Q4 to allow the constant current to pass through the inductive load from left to right side of the inductive load (ZL) so as to generate the constant magnetic field around the inductive load.
Thus, a person skilled in the art may appreciate that the system that generates and controls a constant current to drive an inductive load (ZL), as depicted in Fig. 1 and 2 and as disclosed above may be implemented in such an application where it is required to ensure reasonably a constant proximity sensing device. For example, this invention may be implemented in an application such as proximity sensing for vehicle access to generate constant LF (Low Frequency) magnetic field around a solenoid coil forming an inductive load.
As depicted in Fig. 3, the present invention also provides a method of generating a constant magnetic field around an inductive load. The method starts in step 201 by

receiving, at a driving unit (104), a constant current which is generated from a constant current source (101). Then the method continuous in step 202 to receive, at the same driving unit (104), a control signal from a controller (103). Then finally in step 203, the method drives the inductive load based on said received constant current and the control signal to generate the constant magnetic field around the inductive load. This step of driving the inductive load has been done by using the driving unit (104).
In a given embodiment, the above mentioned step 203 of driving the inductive load based on received constant current and the control signal comprising: allowing, by a driving unit (104), the constant current to flow across the inductive load (ZL); and controlling, by the controller, the driving unit to alter the current flow direction between two opposite sides of the inductive load so that the constant current alternatively pass through the opposite sides of the inductive load between a predetermined interval.
The system and method described above has following technical advancement and/or advantages:
• The present system employs a clever two transistor current limit with built in negative feedback which acts like an ultra-low cost closed loop current controller and thereby avoids costly closed loop current control systems or high wattage LDO (low drop out regulator) based control system with high wattage series resistance as employed in the conventional system.
• Unlike LDO based solution provided in the conventional system, the present system avoids high wattage series resistors limiting the current thus conserving PCB space.
• Tuning is accomplished by Rt1 resistance which is a small low wattage resistor occupying very less PCB space.

Further, the present invention is described with reference to the figures and specific embodiments; this description is not meant to be construed in a limiting sense. Various alternate embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such alternative embodiments form part of the present invention.
Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention.

We Claim:
1. System for generating and controlling a constant current to drive an
inductive load (ZL), comprising:
a power supply;
a constant current source (101) connected in series with the power supply, the constant current source configured to generate a constant current irrespective to any variation in the power supply voltage;
a controller (103) configured to generate a control signal; and
a driving unit (102) coupled to the controller (103) and configured to drive the inductive load based on said control signal using the said constant current.
2. The system as claimed in claim 1, wherein the driving unit configured to drive the inductive load by allowing the constant current to flow across the inductive load (ZL) based on said control signal.
3. The system as claimed in claim 2, wherein the controller configured to control the driving unit to alter the current flow direction between two opposite sides so that the constant current alternatively pass through the opposite sides of the inductive load between a predetermined interval.
4. The system as claimed in claim 1, wherein the driving unit is a H-Bridge.
5. The system as claimed in claim 1, wherein the constant current source (101) is a transistor based current source.

6. The system as claimed in claim 5, wherein the transistor based current source comprises a first transistor (T1), a second transistor (T2), a first resistor (Rt1) and a second resistor (Rt2).
7. The system as claimed in claim 6, wherein both the first and the second transistors are a bipolar junction transistor (T1),
wherein a base terminal of the second bipolar junction transistor is connected to an emitter terminal of the first bipolar junction transistor and a collector of the second bipolar junction transistor is connected to a base of the first bipolar junction transistor,
wherein the control unit is connected at the emitter terminal of the second bipolar junction transistor and the power supply is connected to the collector terminal of the first bipolar junction transistor,
wherein the first resistor is connected between the base and collector terminals of the first bipolar junction transistor and the second resistor is connected between the base and emitter terminals of the second bipolar junction transistor.
8. The system as claimed in claim 6, wherein at least one of the first and second transistors is a MOSFET.
9. A method of generating a constant magnetic field around an inductive load, the method comprising:
receiving, at a driving unit (104), a constant current generated from a constant current source (101);
receiving, at the driving unit (104), a control signal from a controller (103); and

driving, by the driving unit (104), the inductive load based on said received constant current and the control signal to generate the constant magnetic field around the inductive load.
10. The method as claimed in claim 8, wherein driving the inductive load based on received constant current and the control signal comprising:
allowing, by a driving unit (104), the constant current to flow across the inductive load (ZL); and
controlling, by the controller, the driving unit to alter the current flow direction between two opposite sides of the inductive load so that the constant current alternatively pass through the opposite sides of the inductive load between a predetermined interval.